DIE ALIGNMENT WITH CRYSTALLOGRAPHIC AXES IN GaN-ON-SiC AND OTHER NON-CUBIC MATERIAL SUBSTRATES
A semiconductor chip comprises: a semiconductor structure having a single crystal substrate having a non-cubic crystallographic structure and epitaxial layers disposed on the substrate wherein adjacent sides of the semiconductor structure are at oblique angles. A method for separating a plurality of integrated circuit chips. The method includes: providing a semiconductor wafer having single crystal substrate, such substrate having a non-cubic crystallographic structure with an epitaxial layer disposed on the substrate; forming scribe lines at oblique angles to one another in the epitaxial layer; and cutting or cleaving through the substrate along the scribe lines to separate the chips.
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This disclosure relates generally to semiconductor die and more particularly to semiconductor die having non-cubic crystallographic substrates.
BACKGROUNDAs is known in the art, integrated circuits based on Si, GaAs, InP, and other semiconductors are traditionally laid out in rectilinear patterns on the semiconductor wafers. These wafers are single crystals with cubic crystal structures and the crystallographic directions in the plane of the wafer are at 90° angles, which enables scribe and break separation of die with very smooth edges.
More recently, GaN has emerged as the preferred epitaxial material for many applications. In particular, AlGaN/GaN HEMTs grown as epitaxial layers on SiC substrates are incorporated into MMICs (i.e., monolithic microwave integrated circuits having a plurality of transistors, and arranged, for example, formed on a single chip, sometimes also referred to herein as a die) for radar and other multifunction systems. GaN and SiC have hexagonal crystal structures and are therefore fundamentally different from Si, GaAs, InP and other cubic semiconductors with respect to the orientation of the crystallographic axes on the surface of the semiconductor wafer. Hexagonal wafers such as GaN and SiC are typically cut perpendicular to the c-axis as shown in
Despite the fact that the crystallographic axes in GaN and SiC are hexagonal and oriented at 60° and 120° angles, MMIC circuits are traditionally laid out in rectilinear patterns. This precludes the use of “scribe and break” techniques used with cubic structures to give very smooth edges on GaN die (i.e., chips), because the natural cleavage planes for both GaN and the underlying SiC substrate are not aligned with the “streets” or scribe lines that separate MMIC die in the layout. The consequence of this misalignment of MMIC layout and scribe lines with the crystallographic cleavage planes in GaN and SiC is that the MMIC die must be singulated (i.e., separated) with a mechanical sawing process which is time consuming, may damage the material, requires wider streets, and results in die with rough edges. The rough edges are particularly undesirable for high frequency applications that have tight tolerances on MMIC dimensions.
SUMMARYIn accordance with one embodiment of the disclosure, a semiconductor chip comprises: a semiconductor structure having a single crystal substrate having a non-cubic crystallographic structure and epitaxial layers disposed on the substrate wherein adjacent sides of the semiconductor structure are at oblique angles.
In one embodiment, an integrated circuit is formed in the epitaxial layers.
In one embodiment, the substrate is SiC.
In one embodiment, the epitaxial layer includes a layer of GaN on the substrate.
In one embodiment, the epitaxial layer includes a layer of AlGaN on the GaN.
In one embodiment, the epitaxial layer includes a layer of InAlN on the GaN.
In one embodiment, the non-cubic crystallographic structure is a hexagonal crystallographic structure.
In one embodiment, a pair of the sides of the semiconductor structure is at a 60-degree angle.
In one embodiment, a pair of the sides of the semiconductor structure is at a 120-degree angle.
In one embodiment, the semiconductor structure is an equilateral triangular shape.
In one embodiment, the semiconductor structure is a parallelogram shape.
In one embodiment a method is provided method for separating a plurality of integrated circuit chips. The method includes: providing a semiconductor wafer having single crystal substrate, such substrate having a non-cubic crystallographic structure with an epitaxial layer disposed on the substrate; forming scribe lines at oblique angles to one another in the epitaxial layer; and cutting (here cleaving) through the substrate along the scribe lines to separate the chips.
With such structure and method, GaN MMICs are fabricated on AlGaN/GaN epitaxial layers grown on single crystal SiC substrates. The substrates can be of different polytypes (ex: 4H, 6H) with different stacking sequences, but they are hexagonal in structure and are cut or cleaved along crystallographic axes. Scribe and break techniques are used to separate the chips rather then mechanical sawing. The resulting chips have smooth, mirror-like sides.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTIONReferring now to
Each one of the two stages 20, 22 each includes a plurality of the transistors 24, the transistors 24 in each set 20, 22 being distributed along an axis, here indicated as the Y-axis. The Y-axis is, as noted above, at an oblique angle, here 30 degrees, as indicated, to a pair of opposing sides of the integrated circuit chip. Thus, the plurality of transistors is disposed on the integrated circuit chip and distributed along an axis, i.e., the Y axis, making an oblique angle with respect to an axis 23 passing through a side of the integrated circuit chip. Thus, the plurality of transistors is disposed on the integrated circuit chip along an elongated dimension of the chip.
Here, the first stage 20 has two of the FETs 24 and the second stage 22 includes four of the FETs 24. In each stage 20, 22, the FETs 24 therein include a plurality of finger-like control electrodes, here finger-like gate electrodes, G, (
The input-matching network (IMN) 28 is disposed on the integrated circuit chip between a corner 33 of the integrated circuit chip 16a and the plurality of transistors in the input stage (i.e., set 20). The output-matching network (OMN) 32 is disposed between an opposing corner 34 of the integrated circuit chip and the plurality of transistors in the second stage (i.e., set 22).
Next, the integrated circuit chips 16a are formed by etching scribe lines 18″ through the epitaxial layer 10b′ as indicated in
After scribe lines 18′ are formed through the epitaxial layer 10b′ (
It is noted that by cutting along the <2
Referring now to
Each one of the integrated circuit chips 16b, is identical in construction, an exemplary one thereof, here an equilateral triangular shaped chip, being shown in
Next, equilateral triangular shaped integrated circuit chips 16b are formed by etching scribe lines 18″ though the epitaxial layer 10b′.
More particularly, the scribe lines 18′ are along three crystallographic axis directions: the <2
After scribe lines 18″ are formed through the epitaxial layer 10b′ along the three crystallographic axis: the <2
It is noted that with both the triangular shaped chips and the parallelogram shaped chips, the transistors are aligned along an axis at an obtuse angle with respect to a side of the chip; and thus the transistors are distributed along an elongated dimension of the polygon (i.e., the triangle or the parallelogram).
A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, the shape may be trapezoidal. Accordingly, other embodiments are within the scope of the following claims.
Claims
1. A semiconductor chip, comprising: and
- a semiconductor structure, comprising: a single crystal substrate having a non-cubic crystallographic structure;
- epitaxial layers disposed on the substrate; and
- wherein adjacent sides of the semiconductor structure are at oblique angles.
2. The semiconductor chip recited in claim 1 wherein an integrated circuit is formed in the epitaxial layer surface.
3. The semiconductor chip recited in claim 2 wherein the substrate is SiC.
4. The semiconductor chip recited in claim 3 wherein the epitaxial layer includes a layer of GaN on the substrate.
5. The semiconductor chip recited in claim 4 wherein the epitaxial layer includes additional layers AlGaNor InAlNon the GaN.
6. The semiconductor chip recited in claim 1 wherein the non-cubic crystallographic structure is a hexagonal crystallographic structure.
7. The semiconductor chip recited in claim 6 wherein a pair of the sides of the semiconductor structure is at a 60-degree angle.
8. The semiconductor chip recited in claim 6 wherein a pair of the sides of the semiconductor structure is at a 120-degree angle.
9. The semiconductor chip recited in claim 6 wherein the semiconductor structure is an equilateral triangular shape.
10. The semiconductor chip recited in claim 6 wherein the semiconductor structure is parallelogram shaped.
11. The semiconductor chip recited in claim 6 wherein an integrated circuit is formed in the epitaxial layer.
12. The semiconductor chip recited in claim 6 wherein the substrate is SiC.
13. The semiconductor chip recited in claim 6 wherein the epitaxial layer includes a layer of GaN on the substrate.
14. The semiconductor chip recited in claim 11 wherein a pair of the sides of the semiconductor structure is at a 60-degree angle.
15. The semiconductor chip recited in claim 11 wherein a pair of the sides of the semiconductor structure is at a 120-degree angle.
16. The semiconductor chip recited in claim 11 wherein the semiconductor structure is an equilateral triangular shape.
17. The semiconductor chip recited in claim 11 wherein the semiconductor structure is parallelogram shaped.
18. A semiconductor chip, comprising:
- a semiconductor structure, comprising: a single crystal substrate having a non-cubic crystallographic structure;
- and an epitaxial layer disposed on the substrate; and
- wherein adjacent sides of both the epitaxial layer and substrate are at oblique angles.
19. The semiconductor chip recited in claim 18 wherein an integrated circuit is formed in the epitaxial layer surface.
20. A method for separating a plurality of integrated circuit chips, comprising:
- providing a semiconductor wafer having single crystal substrate, such substrate having a non-cubic crystallographic structure with epitaxial layers disposed on the substrate;
- forming scribe lines at oblique angles to one another in the epitaxial layer; and
- cutting through the substrate along the scribe lines to separate the chips.
21. The method recited in claim 20 including forming a plurality of integrated circuits in the epitaxial layer prior to the separating.
22. The method recited in claim 20 wherein a pair of the scribe lines is formed at a 60-degree angle.
23. The method recited in claim 20 wherein a pair of the scribe lines is formed at a 120-degree angle.
24. The method recited in claim 20 wherein the chips are formed as equilateral triangular shaped chips.
25. The method recited in claim 20 wherein the chips are formed as parallelogram shaped chips.
26. The semiconductor chip recited in claim 1 wherein adjacent sides of the semiconductor structure are along crystallographic axes of the substrate.
27. The method recited in claim 20 wherein the cutting is along crystallographic axes of the substrate.
Type: Application
Filed: Jun 7, 2011
Publication Date: Dec 13, 2012
Applicant: Raytheon Company (Waltham, MA)
Inventors: Robert B. Hallock (Newton, NH), Paul M. Head (Dedham, MA)
Application Number: 13/154,968
International Classification: H01L 29/12 (20060101); H01L 21/78 (20060101);